This invention relates to an irrigation water distributing device for directing irrigation water to a plurality of field furrows and, more particularly, relates to a surge irrigation valve.
In the irrigation of crops which are planted in rows, it is common to introduce water at the high end of a field in order that the water may flow by gravity down the furrows to the opposite end of the field. One such method of irrigation is continuous irrigation wherein water is continuously introduced at the high end of the field until the water has reached and has had sufficient time to soak the low end of the field.
However, in many situations, continuous irrigation unevenly distributes irrigation water in the soil which adversely affects plant growth and yields. In particular, water tends to soak in too deeply at the high and low ends of the field and not wetting deep enough in the middle of the field. In order to remedy this situation, continuous irrigation is prolonged which results in a considerable amount of water being wasted in run-off at the low end of the field.
Surge irrigation is an improved method of furrow irrigation that creates a wetting time and a "resting" or recession time on each furrow by cycling water on and off to same in a series of timed increments. During the recession time between alternate wettings, the watered portion of the furrow develops a thin seal on the soil surface reducing the soil's permeability. The formation of the thin seal on the higher end of the field speeds the advance of the water further down the furrow during subsequent wettings. Surge irrigation minimizes unnecessary over-soaking of the high and low ends of the field and minimizes water run-off in attempting to properly soak the middle of the field.
Several theories have been advanced as to how the soil seal in surge irrigation is formed. Continuing research in this field suggests that as the water soaks in, the soil's clods dissolve and settle with the water to form a slick, sealed surface which encrusts by drying during the recession period. In lighter soils, the clay particles in the soil continue to progressively swell even as the flow recedes so that the next surge flow simply finds less infiltration opportunity. A third possible explanation is that as each surge flow recedes, the capillary attraction of the soil and water traps air bubbles that block the small pores of the surface soil and slow down the infiltration of the next surge flow. Whatever the mechanism, the fact remains that the furrow stream advances more quickly over the already wetted soil and slows as it reaches the greater intake demands of drier soil.
In the practice of surge irrigation, farmers are faced with several important considerations when selecting a surge irrigation valve. These are: (1) elimination of water hammer effect, (2) valve pressure drop, (3) minimize electrical and torque requirements of the motorized surge valve, (4) minimize effect of particulate matter, typically sand, entrained in the irrigation supply water, and (5) minimize the number of moving parts.
The water hammer effect is the dynamic increase or decrease of water pressure within the water supply pipes occuring when flow is either terminated or initiated abruptly, respectively. The water hammer effect, if present, has a deliterious effect on the water supply pipes which are typically of concrete or a hard plastic, such as polyvinylchloride (PVC). The rotor valves of U.S. Pat. Nos. 2,506,097; 3,618,637; 3,779,269; and 4,398,562 are deficient in this regard. In particular, each of these rotor valves has a rotor which is mounted for rotation within the valve body and is provided with a substantially L-shaped flow passage formed therethrough. The inlet portion of the rotor is in coaxial alignment with the input or supply port. The outlet portion of the flow passage is positionable, as the rotor revolves, and may be positioned into coaxial alignment with each of the valve outlet ports. However, in transit between valve outlet ports, flow is abruptly terminated; and once in alignment, flow initiates abruptly, thereby creating water hammer effects.
The pressure drop across the valve directly affects system flow throughput, area of irrigation, pump size, and energy requirements. The disc valves of U.S. Pat. Nos. 1,999,804; 2,081,510; 3,108,609; and 4,458,708 with their flow restrictions and multiple flow direction changes would not be acceptable for field irrigation purposes where delivery pressures range from about 4 to about 8 psig. Similarly, butterfly valves are typically designed with flow restrictions, particularly where the butterfly valve seats, thereby reducing the flow rate through such conventional valves.
The third consideration (minimal torque) is related to the pressure force exerted by the irrigation supply water on the internal moving valve member. In most conventional irrigation valves, an electric motor controlled by an automatic sequencer operates the internal valve member to effect the desired cycling of irrigation water. The torque the electric motor is required to supply to operate the valve is in part proportional to the force exerted upon the surface area of the internal valve member normal to the incoming supply water. It should be noted that these valves and distribution pipes are usually located beyond the reach of electric utility lines and must be frequently moved from place to place in the field. Therefore, the valve motors must be powered by a portable source, typically an automotive storage battery. Thus, when the power consumption of the motor is large, the battery must be recharged frequently.
The cylindrical valve member of U.S. Pat. No. Re. 30,224 is unsuitable in this regard. In design, the valve of U.S. Pat. No. Re. 30,224 is hollow with an open bottom coaxial with the water supply and a closed top. Thus, the force exerted is equal to the area of the closed top which forces it upward against the valve housing. Furthermore, since the cylindrical valve member rides on its seals, the radial force of the supply water on the cylindrical wall of the valve member tends to cock or slightly misalign the axis of the valve member with respect to that of the valve housing. Thus, the closed top, the friction of the seals, and cocking of the valve member combine to increase the torque required to rotate the valve member. Butterfly valves also have a large surface area normal to the direction of flow, thereby increasing the torque required to rotate same.
Typically, irrigation water has entrained therein particulate matter such as slit and sand. The particulate matter tends to collect in the bottom of the valve and obstruct or impair the movement of the valve member, thereby increasing motor torque requirements. Although most of the particulate matter tends to fall from the water into the bottom of the interior of the valve body with some hard irrigation waters, all of the surfaces of the interior of the valve become encrusted with mineral deposits with possible embedded fine particulate matter. The accumulation of solid particles and mineral deposits may eventually render the valve inoperable. With irrigation water containing sand or the like, the disc valves mentioned herein would tend to fill up with particulate matter due to the multiple changes in flow direction. The valve of U.S. Pat. No. Re. 30,224, wherein the valve member rides on its seals, would quickly be rendered inoperable due to sand obstructing the valve member's movement. Similarly, butterfly valves would tend to collect sand on the bottom of the valve housing, thereby impeding the movement of the valve member and proper functioning thereof.
Finally, to minimize maintenance efforts, the number and complexity of moving parts should be held to a minimum. For this reason, the disc valves mentioned herein and the irrigation hydrant (butterfly valves) of U.S. Pat. No. 3,011,509 are undesirable.
These, and other limitations and disadvantages of the prior art and especially of the aforementioned patents, are overcome with the present invention and commercially acceptable and competitive embodiments of a surge irrigation valve and the like are herein provided.